new: krb5 krb-as-req parser

packets/krb5.go

@@ -0,0 +1,111 @@
+package packets
+
+import (
+	"errors"
+	"strconv"
+	"time"
+
+	"encoding/asn1"
+	"encoding/hex"
+)
+
+const (
+	Krb5AsRequestType         = 10
+	Krb5Krb5PrincipalNameType = 1
+	Krb5CryptDesCbcMd4        = 2
+	Krb5CryptDescCbcMd5       = 3
+	Krb5CryptRc4Hmac          = 23
+)
+
+//https://github.com/heimdal/heimdal/blob/master/lib/asn1/krb5.asn1
+var (
+	Krb5AsReqParam = "application,explicit,tag:10"
+)
+
+type Krb5PrincipalName struct {
+	NameType   int      `asn1:"explicit,tag:0"`
+	NameString []string `asn1:"general,explicit,tag:1"`
+}
+
+type Krb5EncryptedData struct {
+	Etype  int    `asn1:"explicit,tag:0"`
+	Kvno   int    `asn1:"optional,explicit,tag:1"`
+	Cipher []byte `asn1:"explicit,tag:2"`
+}
+
+type Krb5Ticket struct {
+	TktVno  int               `asn1:"explicit,tag:0"`
+	Realm   string            `asn1:"general,explicit,tag:1"`
+	Sname   Krb5PrincipalName `asn1:"explicit,tag:2"`
+	EncPart Krb5EncryptedData `asn1:"explicit,tag:3"`
+}
+
+type Krb5Address struct {
+	AddrType    int    `asn1:"explicit,tag:0"`
+	Krb5Address []byte `asn1:"explicit,tag:1"`
+}
+
+type Krb5PnData struct {
+	Krb5PnDataType  int    `asn1:"explicit,tag:1"`
+	Krb5PnDataValue []byte `asn1:"explicit,tag:2"`
+}
+
+type Krb5ReqBody struct {
+	KDCOptions            asn1.BitString    `asn1:"explicit,tag:0"`
+	Cname                 Krb5PrincipalName `asn1:"optional,explicit,tag:1"`
+	Realm                 string            `asn1:"general,explicit,tag:2"`
+	Sname                 Krb5PrincipalName `asn1:"optional,explicit,tag:3"`
+	From                  time.Time         `asn1:"generalized,optional,explicit,tag:4"`
+	Till                  time.Time         `asn1:"generalized,optional,explicit,tag:5"`
+	Rtime                 time.Time         `asn1:"generalized,optional,explicit,tag:6"`
+	Nonce                 int               `asn1:"explicit,tag:7"`
+	Etype                 []int             `asn1:"explicit,tag:8"`
+	Krb5Addresses         []Krb5Address     `asn1:"optional,explicit,tag:9"`
+	EncAuthData           Krb5EncryptedData `asn1:"optional,explicit,tag:10"`
+	AdditionalKrb5Tickets []Krb5Ticket      `asn1:"optional,explicit,tag:11"`
+}
+
+type Krb5Request struct {
+	Pvno       int          `asn1:"explicit,tag:1"`
+	MsgType    int          `asn1:"explicit,tag:2"`
+	Krb5PnData []Krb5PnData `asn1:"optional,explicit,tag:3"`
+	ReqBody    Krb5ReqBody  `asn1:"explicit,tag:4"`
+}
+
+// $krb5$Krb5PnData[0].Krb5PnDataValue.Etype$Cname.NameString[0]$Realm$nodata$cipher
+func (kdc Krb5Request) String() (string, error) {
+	var eType, cipher string
+	var crypt []string
+	realm := kdc.ReqBody.Realm
+
+	if kdc.ReqBody.Cname.NameType == Krb5Krb5PrincipalNameType {
+		crypt = kdc.ReqBody.Cname.NameString
+	}
+	if len(crypt) != 1 {
+		return "", errors.New("No crypt alg found")
+	}
+	for _, pn := range kdc.Krb5PnData {
+		if pn.Krb5PnDataType == 2 {
+			enc, err := pn.getParsedValue()
+			if err != nil {
+				return "", errors.New("Failed to extract pnData from as-req")
+			}
+			eType = strconv.Itoa(enc.Etype)
+			cipher = hex.EncodeToString(enc.Cipher)
+		}
+	}
+	if eType == "" || cipher == "" {
+		return "", errors.New("No encryption type or cipher found")
+	}
+	hash := "$krb5$" + eType + "$" + crypt[0] + "$" + realm + "$nodata$" + cipher
+	return hash, nil
+}
+
+func (pd Krb5PnData) getParsedValue() (Krb5EncryptedData, error) {
+	var encData Krb5EncryptedData
+	_, err := asn1.Unmarshal(pd.Krb5PnDataValue, &encData)
+	if err != nil {
+		return Krb5EncryptedData{}, errors.New("Failed to parse pdata value")
+	}
+	return encData, nil
+}